Does AM18x Linux PSP support RTC-only mode?

The Linux PSP does not support RTC-only mode because it is a hardware solution, not software.  To achieve RTC-only mode, the customer will have to cut off power to the core and I/O supply and have just the RTC running.  

--Christina

Hi Christina,

Very thank you for your reply.

I know RTC-only mode is a hardware solution, but I believe the customer is looking for how's S/W to do to keep data working before suspend and after resume.

To make DDR into self-refreash mode should be easy, but how to store and restore the context of the device, like cache、internal registers of SoC...? Does this S/W procedure as same as entering deep sleep mode? Would TI provide some procedure or sample code to make customer to implement it easier?

Thank you.

Since all the power is cut off (except for RTC_CVDD) in RTC-only mode, none of the data/information is saved, except for the RTC time.  When reapplying power to the power rails, you will have to boot the device back up again.  It is not possible to store and restore the content of the device, like deepsleep mode.

--Christina

Dear Christina,

I am confused now, below is a section I copy from chpater 9.7 of AM18x reference guide (SPRUGU4.pdf)

Some limitations apply in the RTC-only mode. First, the RTC_ALARM pin is not available as an option for
use as a control to signal an external power supply to reapply power to the rest of the device. This is
because the RTC_ALARM pin is powered by the I/O supply that is powered down in RTC-only mode.
Second, in RTC-only mode, only the RTC register contents are preserved, all other internal memory and
register contents are lost. Mobile DDR and DDR2 contents can be preserved through the use of
self-refresh (see Section 9.9.2). However, software must be in place to restore the context of the device,
for example, reinitialize internal registers, setup cache memory configurations, interrupt vectors, etc.

In my understanding, above description points out the S/W still has some way to make the system to be restore from RTC-only mode  if the contects of DDR and SoC registers were stored correctly.

Could you clarify this?

Even though the contents of DDR2/mDDR could be preserved, none of the internal memory and register contents are saved.  When coming out of RTC-only mode, the customer will have to perform the same steps as when the board is powered on (power sequence, boot the image, etc). 

Indy Chen said:

However, software must be in place to restore the context of the device,
for example, reinitialize internal registers, setup cache memory configurations, interrupt vectors, etc.

Usually, the "software" is the original boot image that the customer used.  If the customer wants to "restore" the contents by saving off data to the DDR2/mDDR and reloading it back, the customer will have to create their own custom firmware/software.

--Christina

Christina,

Have we (TI) the measured number on EVM or any estimation number for each power mode we support in current Linux PSP? Especially the lowest power consumption we can achieve on current BSP.  I am mot talking about the power sonsumption summary file on WiKi.

It looks like the lowest mode we can achieve right now is not RTC only mode. Customers need to know how low our CPU power consumption will be druing system suspend.

Best Regard,

Rich Chen

TI Sitara FAE

 I, personally, have not taken any measurements on the EVM using Linux.  All the power numbers I have done are based on bare-bone programs to measure only the silicon.  I would recommend posting this particular question on the Linux forum.  The folks there developed the drivers, so they might have more insight on the power measurements.

--Christina